South Korea's defense ministry said Friday that it has launched a crackdown on scores of Web sites that suggest ways to dodge compulsory military service.

The ministry said that it knows of more than 100 such sites and that the crackdown would be carried out in cooperation with police.

"We have sent official letters to major Internet portals such as Daum and Naver to ask for the closure of those illicit Web sites," said ministry spokesman Kim Hyung-Gi.

All able-bodied men must serve in the military for at least two years, and draft-dodging is deep-rooted.

Qualified draftees can avoid military duty if they work for up to 34 months at companies selected by the government to boost the economy. But this system has long been open to abuse, with many sons of the rich and powerful buying their way into firms.

South Korea's 680,000-strong military, backed up by 29,500 US troops, faces off against North Korea's 1.1 million-strong armed forces.